It is common practice in automotive climate control to determine the thermal comfort level of a passenger compartment by drawing a stream of air from the compartment across a sensor to measure the air temperature and to estimate the effect of sun load on the occupants by a solar sensor mounted on top of the instrument panel for exposure to the sun. These measurements are combined with measurements of outside air temperature and engine coolant temperature to supply a control algorithm with the data needed to determine the optimum settings for HVAC mode, blower speed, and mixer door settings which together determine outlet air temperature and air speed needed to achieve a target temperature or comfort setting which is chosen by operator input.
The degree of success in achieving the desired comfort level varies according to specific design parameters including the placement of the solar sensor which for aesthetic reasons may be positioned where it is not the most effective. In any event, the measurement of sun load can be misleading in its computed effect on comfort since the sun direction, passenger clothing and other variables are not readily taken into account.
To avoid the drawbacks of solar load control as well as some objections to the conventional method of obtaining the air temperature, it has been proposed to replace both solar sensing and air temperature measurement with infrared (IR) sensing which directly detects the temperature of the occupant seating area and the occupants themselves. Thus irradiation from seat surfaces, occupant skin and occupant clothing, as well as any object in view of an IR sensor becomes the prime control parameter, and the air temperature in the passenger compartment is not considered at all. While this system affords an improvement over the prior systems by providing better correction for solar load and other sources of radiant energy within a vehicle, under many circumstances this correction can be too much, causing the system to overreact to introduction of hot sources. The air temperature has an effect on comfort and the system performance can be improved by including that measurement in the control algorithm.
Dual zone or multiple zone HVAC systems are already known to supply outlet air at different temperatures to different locations in the vehicle in accordance with individual temperature settings at each location. For example, the driver and passenger may have separate controls and separately managed air outlets. In the prior multiple zone systems the same temperature parameters, except for the selected target temperatures, are used to determine each air outlet temperature. The use of IR sensors, however, make it possible to improve those systems by separately measuring the irradiation from each zone.
It has been recognized that a major cause of discomfort during hot sunny days is that when a vehicle is idle, the interior can become extremely hot, so that upon first entering the vehicle the heat seems to be intolerable. The use of IR sensors make it practical to realistically monitor in-car temperatures even when the vehicle is not in operation and to prevent excessive temperatures by turning on ventilation.